Because only this molecule has the most stable structure.

In any case, it is almost impossible to synthesize regular tetrahedron+high strength bond energy with other materials higher than it.

A diamond is the hardest as long as its molecules are perfect.

Let me show you an article about abrasives, because the strength of many molecules can be improved to.

So it is unlikely to have a stable ranking.

First, natural abrasives

All materials that can be used for grinding or grinding in nature are collectively called natural abrasives. Commonly used natural abrasives are as follows:

1. Diamond

Diamond is the hardest substance known at present, with a microhardness of 98.59Gpa. Diamond is an allotrope of carbon, which is mainly composed of carbon and contains 0.02~4.8% impurities, with a specific gravity of 3. 15~3.53g/cm3. Its origin is very limited, not only expensive, but also extremely scarce.

Diamonds are black, dark brown, grayish black and so on. Due to different impurities. It is brittle and easy to crack along the crystal surface. The larger the crystal, the stronger the ability to resist external forces. The unit of measurement for diamonds is carat, 1 carat = 0.2g ..

As an abrasive, natural diamond has two main uses:

(1) used for dressing grinding wheel;

(2) Grinding and grinding difficult-to-process materials (such as cemented carbide, precious stones, glass, stone, etc.). ).

2. Natural corundum

The main mineral component of natural corundum is α-Al2O3, with a microhardness of 20.58Gpa and a specific gravity of 3.93~4.00g/cm3. There are three kinds of natural corundum in nature:

(1) High-quality corundum (commonly known as gem) includes sapphire (containing titanium) and ruby (containing chromium);

(2) Ordinary corundum, black or brownish red;

(3) Emery, which can be divided into emerald emery and limonite emery, is an aggregate crystal with low hardness.

Among the above three kinds of natural corundum, the first one is mainly used for jewelry, and the latter two can be used as abrasives to make grinding wheels, whetstone, sandpaper, emery cloth or micropowder, grinding paste, etc.

3. Garnet

The crystal form of garnet is good, and its microhardness is 13.33Gpa. There are many kinds of minerals belonging to garnet, but only one kind of iron-aluminum garnet is suitable as abrasive, and its mineral composition is 3FeO. The content of Al2O3.3SiO2 is not less than 85~90%.

4。 quartz

The timely chemical composition is SiO2, which is often mixed with Al2O3, Fe2O3, CaO MgO Fe2O3, etc. The microhardness is 8.04 Gpa, and the timely minerals that can be used as abrasives include vein-like timely, quartzite and quartz sand.

With the development of science and technology, there are dozens of kinds of artificial abrasives, and natural abrasives have been replaced by more and more artificial abrasives because of their own defects. At present, except natural diamond and garnet, other kinds of natural abrasives are rarely used.

Second, artificial abrasives.

Artificial abrasives are divided into corundum series, cemented carbide series and superhard series. The manufacturing methods, characteristics and grinding objects of various abrasives are briefly described as follows.

1. corundum series artificial abrasives

Artificial abrasives belonging to corundum system include brown corundum, white corundum, zirconium corundum, microcrystalline corundum, single crystal corundum, chromium corundum, praseodymium neodymium corundum, black corundum and alumina sintered corundum.

(1) brown corundum (a)

Brown corundum is made from bauxite, anthracite and iron filings by high temperature smelting in electric arc furnace. In the smelting process, the carbon in anthracite reduces the impurities such as silicon oxide, iron oxide and titanium oxide in bauxite to metals, and combines them to form ferroalloys. Because their specific gravity is higher than that of corundum melt, they will settle to the bottom of the furnace and separate from corundum melt. Corundum melts quickly and only a small amount of impurities are mixed in.

The main mineral composition of brown corundum is physical corundum with cubic system, and a small amount of mineral impurities are: calcium silicate, plagioclase calcium, mullite, titanium, glass body and a small amount of iron alloy.

Brown corundum is a widely used abrasive with strong crushing resistance, oxidation resistance, corrosion resistance and good chemical stability. It is suitable for grinding metal materials with high tensile strength, such as fine grinding of ordinary carbon steel, hard bronze and alloy steel, and grinding threads and gears. White corundum can also be used for precision casting and advanced refractories.

(3) Chromium corundum (PA)

Cr ~ (2+) is introduced into Cr ~ (2+) to improve the toughness of abrasive. Its toughness is higher than that of white corundum, but its hardness is similar to that of white corundum. When it is used to process high toughness materials, its processing efficiency is higher than that of white corundum, and the surface smoothness of the workpiece is better. Cr3+ is suitable for processing high toughness workpieces, such as hardened steel, alloy steel, precision measuring tools and instrument parts.

(4) microcrystalline corundum

The raw materials and smelting methods of microcrystalline corundum are basically the same as those of brown corundum. Immediately after stopping the furnace, the molten liquid is poured into the branch mold by banishing or dumping, and cooled quickly (usually within 30 minutes), thus obtaining an aggregate of fine crystals.

In the smelting process of microcrystalline corundum, the reduction degree of impurities is poor, the Al2O3 content is 94-96%, the grain size is generally 80-300 microns, and the crystal accounts for 57-85%, and the maximum grain size does not exceed 400-600 microns. It has the characteristics of high strength and toughness. Suitable for heavy load grinding, which can grind stainless steel, carbon steel, bearing steel and special ductile iron. Because the abrasive particles are in the state of micro-blade breakage during grinding, they are also used for precision grinding and even mirror grinding.

(5) single crystal corundum

Single crystal corundum is made of bauxite, anthracite, iron filings and pyrite, and is melted in an electric arc furnace. Iron oxide, silicon dioxide and titanium oxide in bauxite are successively reduced to form ferroalloy, which settles from the melt to the bottom of the furnace. A small amount of alumina reacts with carbon and ferrous sulfide to produce a small amount of aluminum sulfide filled between single crystal particles. When the frit is cooled and put into water, the aluminum sulfide dissolves, and the single crystal corundum precipitated from the aluminum sulfide can be dispersed to become an abrasive with natural particle size.

Single-crystal corundum is grayish white, the particle shape is mostly equal, the crystal contains no impurities and has angular cutting edges. Under the same grinding force, the moment formed is smaller than that of other abrasives, so it is not easy to break and has high mechanical strength. The compressive strength of single particle is 22~38kg, while that of brown corundum is only 10 ~ 20k g. Single-crystal corundum has high hardness and toughness, so it has strong cutting ability, and can be used to process difficult-to-grind materials with high toughness and hardness, such as tool steel, alloy steel, stainless steel and high barium steel.

(6) Zirconium corundum

Zirconium corundum is made from alumina powder and zircon by high temperature melting in electric arc furnace. The whole process is basically a melting and recrystallization process. It is a * * * crystal aggregate composed of α-Al2O3 and ZrO2. When melting, the two crystals should be staggered as much as possible to form microcrystalline crystals.

Zirconium corundum is suitable for high-speed and heavy-load grinding, which can be used for grinding cast iron, cast steel, alloy steel and high-speed steel, especially for grinding titanium alloy, heat-resistant alloy, high vanadium steel and stainless steel.

(7) praseodymium neodymium corundum (sodium)

The manufacturing process of Pr-Nd corundum is similar to that of white corundum, except that about 0. 1.75% of Pr-Nd concentrate (praseodymium oxide, neodymium oxide and lanthanum oxide) is added in the smelting process. A large number of grinding tests have proved that its grinding performance is better than that of white corundum, and it is suitable for grinding stainless steel, high speed steel, ball-milled cast iron, high manganese cast steel and some heat-resistant alloys.

(8) Black corundum (barium)

The smelting method of black corundum is the same as that of brown corundum. Made of gibbsite and a small amount of reducing agent, the power consumption is about two-thirds of that of brown corundum. Black, main chemical composition: Al2O3 not less than 77%, SiO2 content 10~ 12%,

The content of Fe2O3 is 7~ 10%, the content of TiO2 is about 3%, and the specific gravity is not less than 3.6 1.

Black corundum has good self-sharpening, less calorific value during grinding and good workpiece finish. It is suitable for polishing the bottom of parts before electroplating, polishing aluminum products and stainless steel, polishing optical glass and processing wood. Because of its good hydrophilicity, it can be used to make sandpaper, emery cloth and resin abrasives, as well as grinding paste and polishing powder. Black corundum is not suitable for making ceramic abrasives because of its high iron content.

(9) Alumina sintered corundum

Bauxite sintered corundum is the only corundum that is not smelted by electric furnace. It is made of high-quality bauxite (Al2O3 content is more than 85%) by wet ball milling into 3 micron particle slurry (binder should be added during ball milling), then pressed into abrasive particles with various geometric shapes and sintered at 1500℃.

The main chemical components of bauxite sintered corundum are Al2O3 (85-88%), SiO2 (3-4%), TiO2 (3.5-4.5%) and Fe2O3 (5.6-6.5%). It has α-Al2O3 microcrystal structure, high toughness, can withstand large grinding pressure without breaking, can cut thick metal layers, and the transverse feed can be as high as 6mm or more. The shape of abrasive can be made into various cylinders, which is the only special case among all abrasives and is suitable for heavy-duty rough grinding.

2. Carbide series artificial abrasives

(1) carbonized cinnamon

Silicon carbide is an artificial abrasive made of timely and petroleum coke as main raw materials, gouache and salt as auxiliary materials, which are evenly mixed in a certain proportion and then put into a resistance furnace for high temperature melting.

There are two kinds of silicon carbide: black silicon carbide is black or blue-black, and green silicon carbide is green or turquoise. In the manufacturing process, the production of green silicon carbide is characterized by the use of pure raw materials and the addition of salt to the furnace charge, which can promote the greening of products. The purity of green silicon carbide is higher than that of black silicon carbide.

Silicon carbide does not react with any acid, but the melting of basic oxides can promote the decomposition of silicon carbide.

Compared with corundum artificial abrasive, black silicon carbide has higher hardness and greater brittleness, and is suitable for processing metallic and nonmetallic materials with lower tensile strength, such as gray cast iron, brass, lead and other nonferrous metals, as well as hard and brittle materials such as ceramics and glass factory materials.

Compared with black silicon carbide, green silicon carbide has higher purity, hardness and brittleness, and is suitable for processing hard and brittle materials, such as cemented carbide, glass and agate. It is also widely used in the fine grinding of measuring tools, cutters and molds and honing of engine cylinders such as airplanes, automobiles and ships.

With the development of industry and the progress of science and technology, the non-abrasive use of silicon carbide is expanding. In terms of anti-inflammatory materials, it is used to make various advanced anti-inflammatory products, such as backing plates, tapholes, crucible molten pools and so on. As a deoxidizer in metallurgical industry, it can save electric energy, shorten smelting time and improve operating environment. In the electrical industry, silicon carbide is used to make heating elements-silicon carbon rods. Sintered products of silicon carbide can be used as fixed resistance and antiskid preservative in engineering. Silicon carbide mixed with epoxy resin can be coated on acid-resistant containers and worm wheel blades, which plays a role in corrosion resistance and wear resistance.

(2) Cerium silicon carbide (CC)

Cerium silicon carbide is smelted by adding a small amount of cerium oxide (CeO2 _ 2) into silicon carbide charge without adding salt. Its appearance is similar to that of green silicon carbide, and its microhardness is 36.29Gpa. Compared with green silicon carbide, its cerium silicon carbide has higher microhardness, single particle compressive strength and toughness.

Because the physical properties of cerium silicon carbide are bent, its grinding effect is also improved to some extent. Experiments show that the cutting efficiency of cerium silicon carbide is nearly twice as high as that of green silicon carbide when grinding titanium alloy, and the spark is small. When grinding cast iron, when the feed speed is 0.0 1mm, the durability of cerium silicon carbide is 18.9% higher than that of green silicon carbide grinding wheel, and the grinding ratio is 9.6% higher. When the feed rate is 0.02mm, the durability is increased by 27.4% and the grinding ratio is increased by 74. 1%. It can be seen that the effect of grinding cast iron feed with cerium silicon carbide is more obvious than green silicon carbide. The grinding effect of cemented carbide is similar to that of green silicon carbide, and the grinding effect of high-speed steel such as CO5Si M5Al 5F-6 is similar to that of single crystal corundum.

(3) boron carbide

Boron carbide (B4C) is made by melting boric acid (H3BO3) and carbon materials in an electric arc furnace at the high temperature of 1700~2300℃, and the molten boric anhydride (B2O3) is directly reduced by carbon.

Boron carbide is a kind of gray-black powder with metallic luster and a superhard material. When heated to 500℃ in air, boron carbide begins to oxidize, and its oxidation effect is more obvious when the temperature reaches 800~900℃. Boron carbide has been used to replace diamond in grinding cemented carbide tools. Its sintered products can replace diamond as a dressing tool for grinding wheels, and are suitable for finely grinding hard materials such as C-W alloy, C-Ti alloy, sintered corundum, artificial gem and special ceramics.

(4) carbon, silicon and boron

Silicon-boron alloy is made of boric acid, quartz sand and graphite by high temperature melting in electric arc furnace. It is grayish black, and its hardness is lower than that of boron nitride and higher than that of boron carbide. Brittle, suitable for processing hard materials such as cemented carbide, semiconductor, artificial gem and special ceramics.

3. Superhard series artificial abrasives

(1) diamond (small)

Diamonds are made from stone black and some metals or alloys as catalysts. At high temperature (1000~2000℃) and high pressure (557~608Mpa), the graphite structure is transformed into diamond structure. Diamond is the hardest substance known, with high compressive strength, good thermal conductivity, chemical stability, wear resistance and strong cutting ability.

Diamonds can be divided into five grades: JR 1, JR2, JR3, JR4 and JR5. Its characteristics and uses are as follows:

Model 1. JR 1: Most of the crystals are needle-like with rough crystal faces. It is used to manufacture resin-bonded diamond abrasives, mainly used for fine grinding of cemented carbide, ceramics, glass and refractory materials, with good processing effect and high surface gloss. Sometimes it is used for semi-fine grinding, but it is not suitable for heavy load grinding.

2.JR2 type: Most of the crystals are equal-area crystals, which are suitable for manufacturing diamond abrasives with metal bond and ceramic bond. It can bear a large load, and can be used for rough grinding and semi-fine grinding of cemented carbide and non-metallic materials, and can also be used for cutting optical glass, precious stones, high-hardness rocks and so on.

3.JR3 type: relatively complete crystal, smooth crystal face and high compressive strength. It is used to manufacture metal-bonded geological drill bits, dressing tools and cutting tools.

4.JR4 type: The crystal is complete, and the compressive strength is higher than JR3 type, which is used to manufacture geological drills, mineral processing tools and cutting tools.

5.JR5 type: the particles are light yellow or light yellow-green, mostly transparent and complete octahedral crystals, with no impurities and high strength. Suitable for manufacturing cutting saw blades, drill bits and dressing tools. Used for processing hard and brittle nonmetallic materials.

(2) Cubic boron nitride

Cubic boron nitride (CBN) is a kind of cubic boron nitride with hexagonal boron nitride as raw material and metal reduction or alkaline earth metals or their nitrides as catalysts, which is transformed into cubic crystals at high pressure and high temperature. This transformation is similar to the transformation of graphite into diamond.

Cubic boron nitride (CBN) is a new type of superhard abrasive. Its hardness is second only to that of diamond, but its thermal stability and chemical stability are better than that of diamond. In particular, it has good chemical inertness to iron group metals and is not easy to react with steel. It has unique advantages in grinding hard and tough steel, and its wear resistance is 30~40 times higher than that of ordinary abrasive. When processing high-speed steel, alloy steel and heat-resistant steel, its processing ability greatly exceeds that of diamond abrasive. It can also be used for grinding cemented carbide and nonmetallic materials.